The present invention relates to sliders of magnetic hard disk drives. More specifically, the present invention relates to the manufacture of sliders for hard disk drives.
Hard disk drives are common information storage devices essentially consisting of a series of rotatable disks that are accessed by magnetic reading and writing elements. These data transferring elements, commonly known as transducers, are typically carried by and embedded in a slider body that is held in a close relative position over discrete data tracks formed on a disk to permit a read or write operation to be carried out. In order to properly position the transducer with respect to the disk surface, an air bearing surface (ABS) formed on the slider body experiences a fluid air flow that provides sufficient lift force to “fly” the slider and transducer above the disk data tracks. The high speed rotation of a magnetic disk generates a stream of air flow or wind along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow cooperates with the ABS of the slider body which enables the slider to fly above the spinning disk. In effect, the suspended slider is physically separated from the disk surface through this self-actuating air bearing.
Some of the major objectives in ABS designs are to fly the slider and its accompanying transducer as close as possible to the surface of the rotating disk, and to uniformly maintain that constant close distance regardless of variable flying conditions. The height or separation gap between the air bearing slider and the spinning magnetic disk is commonly defined as the flying height. In general, the mounted transducer or read/write element flies only approximately a few nanometers above the surface of the rotating disk. The flying height of the slider is viewed as one of the most critical parameters affecting the magnetic disk reading and recording capabilities of a mounted read/write element. A relatively small flying height allows the transducer to achieve greater resolution between different data bit locations on the disk surface, thus improving data density and storage capacity. With the increasing popularity of lightweight and compact notebook type computers that utilize relatively small yet powerful disk drives, the need for a progressively lower flying height has continually grown.
As shown in FIG. 1 an ABS 102 design known for a common catamaran slider 104 may be formed with a pair of parallel rails 106 and 108 that extend along the outer edges of the slider surface facing the disk. Other ABS 102 configurations including three or more additional rails, with various surface areas and geometries, have also been developed. The two rails 106 and 108 typically run along at least a portion of the slider body length from the leading edge 110 to the trailing edge 112. The leading edge 110 is defined as the edge of the slider that the rotating disk passes before running the length of the slider 104 towards a trailing edge 112. The leading edge 110 may be tapered despite the large undesirable tolerance typically associated with this machining process. The transducer or magnetic element 114 is typically mounted at some location along the trailing edge 112 of the slider as shown in FIG. 1. The rails 106 and 108 form an air bearing surface on which the slider flies, and provide the necessary lift upon contact with the air flow created by the spinning disk. As the disk rotates, the generated wind or air flow runs along underneath, and in between, the catamaran slider rails 106 and 108. As the air flow passes beneath the rails 106 and 108, the air pressure between the rails and the disk increases thereby providing positive pressurization and lift. Catamaran sliders generally create a sufficient amount of lift, or positive load force, to cause the slider to fly at appropriate heights above the rotating disk. In the absence of the rails 106 and 108, the large surface area of the slider body 104 would produce an excessively large air bearing surface area. In general, as the air bearing surface area increases, the amount of lift created is also increased. Without rails, the slider would therefore fly too far from the rotating disk thereby foregoing all of the described benefits of having a low flying height.
The current slider manufacturing technique involves diamond related machining processes such as slicing, grinding, lapping, and dicing. The dicing process in particular is very critical, often performed by using a circular diamond saw blade rotating at high speeds with a constant feed of coolant water to reduce the temperature of the working material.
During this dicing process, the edges 116 along the diced surface are subjected to mechanical deformation forming ridges along the slider's edge. The amount of deformation is typically in the range of 10 to 15 nm in height depending upon machining parameters such as feed rate, blade quality, and others. This slider edge ridge could also lead to catastrophic failures at the head disk interface if they become higher than the ABS of the slider. This problem rises exponentially with decreasing form factor of the drive head, such as from PICO to FEMTO sliders.
Another major problem of the conventional diamond-sawing process is the generation of micro-cracking or fracturing along the edges of the slider as a result of heat generated during machining. When built into the drives, these could behave as nucleus points for fracturing during thermal or mechanical shock loading of the slider. With the slider capacity ever increasing and the fly height of the slider continuously decreasing, this becomes an undesirable defect.
Substrate particle generation is also a key problem that potentially arises due to the micro-cracking and fracturing of the slider edges of the substrate. These particles could arise from the leading edge and the diced edges of the ABS as a result of dicing.
One approach to minimize these problems could be by optimizing the cutting parameters on the dicing machine, such as feed rate, coolant flow, and spindle rotation speed. With this method, the amount of buildup and micro-cracks could be reduced to a certain extent but can never be eliminated since there will always be some amount of deformation and fracture as a result of the cutting mechanism.
In an alternate method, a laser is used to apply heat to the dicing edge 116 of the slider and thus altering the stress levels as a result of which the slider edge ridge is shifted below the ABS of the slider. Since this process also alters slider curvature, both crown and cross crown, the process can compensate for the slider ridge only if the curvature required by the slider is higher than that of the ridge. With the advancement in the ABS designs, the fly-height could become virtually insensitive to the slider curvature or require sliders without any curvature. Also this technique does not address particle generation due to the leading edge, which could become a source for particle pull out. Another technique changes the slider 104 curvature by heating the backside of the slider with a laser to change the slider curvature and in turn altering the slider edge ridges below the ABS surface.
Most of the previously mentioned techniques use conventional continuous or pulsed lasers to ablate the slider material. One of the major problems associated with these lasers is the amount of localized heat that is generated. This heat could lead to re-positioning of the material and further initiate micro-cracking and fracturing of the edges that could propagate into calamitous failures in the drive level.
As stated above, the dicing process is a critical step in the slider fabrication since it is the last machining step in the line before the head gimbal assembly (HGA) manufacturing process begins. As shown in FIG. 2, the dicing step leaves mechanical stresses and deformations 202 along the edges 116 of the air bearing surfaces (ABS) 102. These deformations 202 could be a result of build up of compressive stresses at the ABS 102 due to previous processes such as lapping. With the disk storage density continuously increasing, the demand for the slider to fly closer to the disk surface also increases. If the deformations 202 at the slider edge 116 happen to be higher than the ABS, this could lead to catastrophic failures in the disk drives.